CVE-2021-33626

Local code execution via unchecked SMM communication buffer

Published Oct 1, 2021 · Updated Aug 11, 2026

Memory corruption in affected Siemens industrial PC BIOS releases allows local users to execute code through an SMM handler. The PnpSmm, SmmResourceCheckDxe, and BeepStatusCode drivers accept CommBuffer and CommBufferSize values without ensuring that the referenced range stays outside protected SMRAM. An attacker must already be able to run low-privilege untrusted code locally; successful exploitation can corrupt firmware or operating-system memory and execute code in SMM.

CVSS severity7.8
High
EPSS probability0.31%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Memory corruption in affected Siemens industrial PC BIOS releases allows local users to execute code through an SMM handler. The PnpSmm, SmmResourceCheckDxe, and BeepStatusCode drivers accept CommBuffer and CommBufferSize values without ensuring that the referenced range stays outside protected SMRAM. An attacker must already be able to run low-privilege untrusted code locally; successful exploitation can corrupt firmware or operating-system memory and execute code in SMM.

The record

CVE
CVE-2021-33626
Published
Oct 1, 2021
Updated
Aug 11, 2026
Vendor
Siemens
Product
SIMATIC IPC477E PRO
Classifications
CWE-829, T1068
Attack vector
local
Privileges
authenticated

Timeline

How it unfolded

  1. Oct 1, 2021CVE publishedPublication date reported by the CVE source.
  2. Aug 11, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=0 <V21.01.17

What conditions does exploitation require?

Attack vectorlocal
Required privilegesauthenticated

What is affected?

Siemens · SIMATIC IPC477E PROversion=0 <V21.01.17
Siemens · SIMATIC IPC847Eversion=0 <V25.02.12
Siemens · SIMATIC Field PG M5version=0 <V22.01.10
Siemens · SIMATIC IPC377Gversion=0 <V28.01.04
Siemens · RUGGEDCOM APE1808 BIOSversion=0 <V1.0.202N
Siemens · SIMATIC IPC627Eversion=0 <V25.02.12
Siemens · SIMATIC IPC277Gversion=0 <V28.01.04
Siemens · SIMATIC ITP1000version=0 <V23.01.10
Siemens · SIMATIC IPC677Eversion=0 <V25.02.12
Siemens · SIMATIC IPC127E Industrial Edge Deviceversion=0 <V27.01.09
Siemens · SIMATIC IPC427E Industrial Edge Deviceversion=0 <V21.01.17
Siemens · SIMATIC IPC477Eversion=0 <V21.01.17
Siemens · SIMATIC IPC277G PROversion=0 <V28.01.04
Siemens · SIMATIC IPC227G Industrial Edge Deviceversion=0 <V28.01.04
Siemens · SIMATIC IPC327Gversion=0 <V28.01.04
Siemens · SIMATIC IPC647Eversion=0 <V25.02.12
Siemens · SIPLUS IPC427Eversion=0 <V21.01.17
Siemens · SIMATIC Field PG M6version=0 <V26.01.13

Published CVSS scores

7.8Siemens ProductCERTCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
7.8NIST NVDCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
4.6NIST NVDAV:L/AC:L/Au:N/C:P/I:P/A:P

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 9, 2026Sep 15, 2026
Latest reporting daySep 15, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectorlocal
Privilegesauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-829Inclusion of Functionality from Untrusted Control Sphere
T1068Exploitation for Privilege Escalation

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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